I use an otterbox for my smaller PSK and I loved it until about tow months ago. I was bored during a typhoon one day in Japan so I was repacking my gear and I ran a test with my otterbox. I emptied it out and put it in a pitcher full of water for about 30 minutes. When I opened it to check its abilities, it had water in it. I was disappointed, especially due to the price of the box and all, but then I had a thought. This box was fully submerged for over half an hour, and it had water in it. Most everything that was in it would be ok, except of course for the tinder, but most would be fine.
Despite this experiment and in the driving rain of Fuji, Japan, it did hold tight. My only concern would be if I was in a boat that capsized or if I was thrown overboard at sea. A few people here gave me some advise on how to put in another seal, but I have been motivated enough to explore these projects yet.
All in all, I think it does better than an altoids tin for my needs, especially the "crush proofness" of the box itself.
Just my experience,
Garrett
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On occasion of every accident that befalls you, remember to turn to yourself and inquire what power you have for turning it to use. - Epictetus